The subject matter described herein relates generally to methods and systems for controlling a wind turbine, and more particularly, to methods and systems for preventing overspeed of a wind turbine rotor during a misalignment of the wind turbine rotor.
Generally, a wind turbine includes a turbine that has a rotor that includes a rotatable hub assembly having multiple blades. The blades transform wind energy into a mechanical rotational torque that drives one or more generators via the rotor. The generators are sometimes, but not always, rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the rotor for the generator to efficiently convert the rotational mechanical energy to electrical energy, which is fed into a utility grid via at least one electrical connection. Gearless direct drive wind turbines also exist. The rotor, generator, gearbox and other components are typically mounted within a housing, or nacelle, that is positioned on top of a base that may be a truss or tubular tower.
At high winds, high turbulence and/or up-flow, wind turbines may experience outage due to a high yaw misalignment. The yaw moment induced by the rotor cannot longer be counteracted by the yaw system and yaw runaway may be observed. In this event, the control system of the wind turbine may try to compensate lowering of rotor speed and power losses resulting form the yaw misalignment. Under fluctuating wind conditions this may in turn result in an unwanted overspeed of the rotor.
In view of the above, there is a desire for improved controlling of wind turbines during yaw misalignment.